Frequency converter for different mains voltages

Abstract

The invention is directed to controlling an electric motor by means of a frequency converter. The frequency converter can be connected to one of several different mains voltages. According to the present invention, the maximum output power of the frequency converter, is limited when the actual mains voltage is lower than the maximum nominal mains voltage, for which the frequency converter is designed, and during the limitation the frequency converter controls the speed of the motor within a power range up to a limited maximum output power. This gives a genuine multi-voltage unit, which can be connected to a wide range of mains voltages.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Application No. PCT / DK02 / 00785 filed on Nov. 21, 2002, Danish Patent Application No. PA 2001 01750 filed on Nov. 23, 2001 and Danish Patent Application No. PA 2001 01751 filed on Nov. 23, 2001.FIELD OF THE INVENTION[0002]The invention concerns a frequency converter, which can be connected to one of several different mains voltages, and a method for speed control of an electric motor by means of a frequency converter.BACKGROUND OF THE INVENTION[0003]Differences in the mains voltages in the USA and Europe increase the production costs, as product differentiation is required. For years, therefore, it has been known to make frequency converters, which can be connected to different mains voltages, see for example U.S. Pat. No. 4,656,571.[0004]However, this gives rise to a problem, when a frequency converter is connec...

AI Technical Summary

Benefits of technology

[0010]Based on the above, the object of the invention is to design a general purpose frequency converter, which electrically can adapt, or can easily be adapted, to its surroundings.

[0011]According to the invention, this task is solved by a method where a DC / DC converter placed between a rectifier and an inverter is regulated to output a DC voltage that is kept constant during operation at each one of the several mains voltages, that a limit value signal is compared with one ore more measured or calculated parameters, that a control device limits the maximum output power by reducing the motor frequency generated by the inverter, and that the frequency converter, during a limitation of an output power of from the inverter, controls the speed of the electric motor within a power range up to the limited maximum output power.

Problems solved by technology

Imagining that a frequency converter according to the state of the art is connected between a motor and a weak mains, and the weak mains has a lower voltage than expected, this will cause an increased current sink from the mains, which again results in a voltage drop, etc.

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